1. Field of the Invention
The present invention relates generally to implantable orthopedic prostheses for replacing human skeletal joints, and surgical instruments for implanting such prostheses, and relates more particularly to surgical instruments for preparing human bones to receive implantable orthopedic prostheses.
2. Background of the Related Art
Implantable orthopedic prostheses, in one form, comprise man-made replacements for the ends and articulating surfaces of the bones of the skeleton. Such prostheses are implanted to repair or reconstruct all or part of an articulating skeletal joint that is functioning abnormally due to disease, trauma, or congenital defect. Among the various articulating skeletal joints of the human body that are eligible to be fitted with implantable orthopedic prostheses, the hip, knee and shoulder joints are most often treated with such prostheses. The performance of each of these joints has an important effect on quality of life. The hip and knee joints play a critical role in ambulation and the shoulder joint plays a critical role in manual dexterity, resulting in great demand for surgical correction of abnormalities of these joints.
As used herein, the words proximal and distal are terms of reference that indicate a particular portion of a bone or prosthesis component according to the relative disposition of the natural bone or implanted prosthesis. Proximal indicates that portion of a component nearest the torso, whereas distal indicates that portion of a component farthest from the torso. Directional terms of reference used herein include superior, inferior, anterior, posterior, medial and lateral, which are used according to their commonly understood anatomical meanings. More particularly, with regard to a person in a standing position, superior means upward, inferior means downward, anterior means forward, posterior means rearward, medial means inwardly from the side toward the center of the body, and lateral means outwardly from the center of the body toward the side.
The human knee joint involves three bones: the femur, the tibia and the patella, each having a smooth articulation surface arranged for articulation against an adjacent articulation surface of one or more of the other bones. The femur includes at its distal extremity two spaced, generally convex condyles, comprising a medial and a lateral condyle, having an intercondylar groove therebetween extending generally in the anterior-posterior direction. The anterior end of the intercondylar groove extends up the anterior face of the distal femur to form a shallow patellar groove. The tibia includes at its proximal extremity a tibial platform comprising two spaced, generally convex meniscal surfaces disposed in opposition to the medial and lateral condyles of the distal femur, and forming articulating surfaces against which the condylar articulating surfaces of the distal femur articulate. The patella, attached via the patellar tendon to the tibia and femur, has a generally convex posterior articulating surface that articulates against the patellar groove of the anterior distal femur.
As a result of disease, congenital defect, or trauma, one or more of the articulating surfaces of the bones comprising the knee joint may fail to function properly. In that event, surgical intervention is sometimes necessary to restore function. One such surgical intervention involves implanting a total knee prosthesis, in which at least the tibial and femoral articulating surfaces are replaced with prosthetic articulating surfaces. Often, the posterior articulating surface of the patella is also replaced with a prosthetic articulating surface. In such surgery, the ends of the affected bones of the knee joint are resected to provide a stabile bony surface of predetermined geometry against which the prosthetic articulating surfaces can be secured. The placement of the resection cuts is critically important to insure that after the prosthetic components are implanted, the stability of the knee, as controlled by soft-tissue, and the kinematics of the knee will be restored to an anatomically correct condition. It is customary, therefore, to provide specialized instrumentation to assist the surgeon in properly locating all resections of the bones of the knee joint, with the instrumentation being specially configured for the prosthesis that is to be implanted.
To help assure that the femoral and tibial components of the prosthetic knee are properly aligned and spaced to restore the knee joint to an anatomically correct condition, it is useful to provide a common reference datum for controlling the location of the resections of the distal femur and proximal tibial. One known method for providing a reference datum is to temporarily fix an instrument in the medullary canal of either the femur or the tibia for supporting or positioning other instruments, such as cutting blocks, to guide the resection cuts. It is known to place a bullet-shaped reamer in the medullary canal to provide such a reference datum. Another known technique includes placing an intramedullary rod in the medullary canal and using adapter sleeves positioned around the rod, which aid in aligning the cutting instruments. Also known is the technique of assembling a stem trial directly to the cutting instrument.
Certain disadvantages of the prior techniques discussed above have been noted. Bullet reamers will sometimes snake down the medullary canal, resulting in a false representation of the canal center, and therefore, misguided cuts. Bullet reamers typically have a short cutting section at the end, followed by a shank of reduced diameter. Such reamers provide only a limited length of engagement with the medullary canal. Because of the short engagement length, the reamer can be unstable as a reference datum. The use of adapter sleeves in conjunction with an intramedullary rod requires a different sleeve for each size of stem. Using an intramedullary rod alone foregoes the benefit of using a stem trial that is appropriately sized to fit the canal that has been reamed to receive a particular stem size. Assembling the stem trial directly to the cutting block requires multiple assembly steps when the surgical technique requires changing cutting blocks. In order to change cutting blocks, the stem trial and attached cutting block must both be removed from the patient, then disconnected from one another, then the stem trial must be reattached to the new cutting block.
Accordingly, it would be desirable to provide an intramedullary reference datum that is stabile and that enhances the accuracy and reproducibility of the resection cuts required for implanting an orthopedic prosthesis. The present invention, a particular embodiment of which is shown and described below, provides these and other desirable advantages.